Compositions that may be used to thermally insulate other materials, especially from the effect of intense sunlight, have a number of potential applications: Examples include among others:
a) Insulation of structures (e.g. a house or hotel) to reduce energy consumption, especially during summer months in southern regions.
b) Insulation of flooring material (such as wood or concrete) to reduce the temperature, thus allowing, for example, bare-foot passage on a patio or deck.
c) Insulation of heat sensitive equipment such as is used in military and civilian applications, allowing improved operational efficiency by reducing the influence of heat on internal components under arduous conditions, such as desert environment.
The invention describes a method of preparing a paint system (paint or paint plus primer) which offers a solution to the problem of solar heating. Moreover the material may be applied by conventional methods, such as brush, spray or roller, and may be applied during original part preparation or retroactively after a product has been manufactured or placed in service.
Infra red reflecting compositions have been produced using a number of approaches. U.S. Pat. No. 5,006,175 describes a brown rutile pigment composition from about 40 to about 50% by weight of titanium, from about 2.3 to about 4.5% by weight of manganese, from about 7.3 to about 11% by weight of tungsten, from 0.05 to about 5% of lithium and from about 0.1 to about 20% of cerium. Use of the brown rutile pigment is described in rigid vinyl and alkyd paint and is described as infra red reflective between 700-1000 nm.
The patent describes Color values in masstone and tint were tested using a conventional laboratory paint shaker method, dispersing the pigments in an air-dry enamel vehicle, and grinding for 20 minutes on a paint shaker in a glass jar with glass beads. The tint was calculated as 50% pigment and 50% titanium dioxide. The dispersion was then drawn down on a Leneta opacity chart. Color differences were evaluated using the Diano Match-Scan Spectrophotometer and expressed in Hunter values. Tint strength differences were calculated using the K/S figure at 460 nanometers. The differences between the pigment of Example 1 and the pigment of Example A were found to be as follows:
TABLE IIDELDRGYBMasstone:0.18−0.13−0.09−0.09Tint (1:1)0.27−0.260.01−0.07
The results with respect to masstone show insignificant differences between the two pigments. In tint, however, is found that the pigment of Example 1 has a 3% strength advantage over the pigment of Example A, and this is believed to be due to the finer particle size.
Nothing further is described for coating systems. The patent does describe use in PVC sidings as follows: one desirable characteristic of the pigments and other additives that are blended with the vinyl chloride is their ability to reflect infra red rays. A highly infra red reflective siding will remain cooler when exposed to sunlight than a siding containing additives which readily absorb many of these infra red rays. Lower temperatures mean a lower heat build-up within the structure and longer life for the siding. A reduction of a few degrees in the heat build-up translates into a substantial increase in the life of the siding. No further quantification of the infra red reflectivity effect is described or how to formulate to maximize the effect.
U.S. Pat. No. 5,607,995 describes a paint composition which comprises a binder to impart film forming properties compounded with quasi transparent polyolefin filler particles having a particle size below 110 micrometers, said polyolefin being selected from the group consisting of a polyethylene, a polypropylene, copolymers of ethylene and propylene and mixtures thereof, said polyolefin filler particles being present in an amount between 0.1% to 10% by weight of the composition. These paint compositions were found to possess low gloss and matte properties at visible and high reflectance in the thermal infra-red wavelengths.
U.S. Pat. No. 5,650,461 describes a paint compositions which provide a Chemical Agent Resistant Coating (CARC), consisting of one layer topcoat paint system, which imparts an increase in the reflectivity at the thermal infra-red region, while controlling the colour in the visible range and are maintaining a low gloss, comprising: an extender selected from polyolefins and substituted polyolefins; a pigment, selected from a metal oxide calcined at a temperature of above 600.degree. C. and a paste of metal flakes and any mixture thereof; a binder consisting of a modified polyurethane resulted from an isocyanate and a co-reactant possessing at least two hydroxy groups, and a solvent system to dissolve the components in the paint composition.
U.S. Pat. No. 5,713,974 describes Evacuated micro-spheres, insulating materials constructed from such micro-spheres, and methods of manufacturing same provide insulation and reduce heat transfer through radiation, conduction and convection. Additionally, an infrared reflective coating is provided on a microsphere surface to reduce radiant heat transfer. A protective exterior coating is also provided to protect an exteriorly applied infrared reflective coating on such a microsphere. Furthermore, the spheroidal geometry of such micro-spheres restricts heat transfer to point-to-point conduction there between. Finally, evacuated micro-spheres further reduce through-heat transfer within a shell. One embodiment utilizes such evacuated micro-spheres in constructing an elastomeric roof coating which appreciably reduces cooling and air conditioning power costs for a building. An alternative embodiment utilizes such an elastomeric coating in constructing an exterior paint for a building. A method of evacuating such micro-spheres involves in-permeation of selected gases within a microsphere that reacts under sufficiently high temperatures with residual gases within the microsphere to produce by-product gases which out-permeate from within the sphere under sufficiently high temperatures. Furthermore, a method of constructing suitable glass microspheres which are suitable for evacuating via out-permeation is also described.
The patent focuses on the method of production of the evacuated micro-spheres and describes their use in an exterior coating formulation as follows: “The evacuated shells 12 provide a crucial component in formulating a coating 32 which allows attainment of appreciably decreased thermal conductivity, and helps develop and retain a high reflectivity to solar and other infra-red radiation. A combination of long-term high IR reflectivity and low thermal conductivity decreases the energy loading, resulting from absorption and transference of heat, into a coated enclosure. For example, such a coating 32 could be utilized within an infra-red oven to retain heat more efficiently therein and enhancing the cooking operation of process.”
The patent itself teaches nothing about specific wavelength effects, nor does it teach how to maximize IR reflectance of a coating or other composite material by formulating with other materials to gain an increased effect.
U.S. Pat. Nos. 6,174,360 B1 and 6,454,848 B2 describe new solid solutions having a corundum-hematite crystalline structure which are useful as inorganic pigments. Solid solutions according to the present invention include a host component having a corundum-hematite crystalline structure which contains as guest components one or more elements from the group consisting of aluminum, antimony, bismuth, boron, chrome, cobalt, gallium, indium, iron, lanthanum, lithium, magnesium, manganese, molybdenum, neodymium, nickel, niobium, silicon, tin, titanium, vanadium, and zinc. Solid solutions according to the present invention are formed by thoroughly mixing compounds, usually metal oxides or precursors thereof, which contain the host and guest components and then calcining the compounds to form the solid solutions having corundum-hematite crystalline structure. Some of the new solid solutions according to the present invention exhibit relatively low Y CIE tri-stimulus values and relatively high near infrared reflectance. The patent suggests these solid solution pigments may be suitable as pigments in the general paint and polymer markets where increased near infrared reflectance would result in low heat build-up and thus lower energy costs.